Automatic relatching circuit breakers



Dec. 10, 1968 F. E. MYERS 3,416,108

AUTOMATIC .RELATCHIN'G CIRCUIT BREAKERS tiled Marh 1e, 1966 s sheets`-sheet 1 ETS- .2 /5/ a 401 i d 42. fd/f 4l f Dec. l0, 1968 F. E. MYERS ACTCMATTC RRLATCRTNC CIRCUIT BREAKERS 3 Sheets-Shee il Filed March 18, 1966 Dec. 10, 1968 E. MYI-:Rs 3,416,108

AUTOMATIC RELATCHING CIRCUIT BREAKERS Filed March 18, 1966 3 Sheets-Sheet 5 l.: E. 5- BY United States Patent O 3,416,108 AUTOMATIC RELATCHING CIRCUIT BREAKERS Felix E. Myers, Haddon Heights, NJ., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Mar. 18, 1966, Ser. No. 535,435 5 Claims. (Cl. 335-37) ABSTRACT OF THE DISCLOSURE An automatic relatching circuit breaker including a small biasing spring arranged to return the cradle of an over-center spring mechanism from its tripped to its off or reset position in response to a tripping operation caused by the occurrence of a fault. Because the main spring of the over-center mechanism is only slightly extended when the cradle thereof is moved from its tripped back to its latched or reset position, the biasing spring for accomplishing such movement of the cradle may `be made relatively small. Furthermore, once the cradle is moved by .the biasing spring from the '"tripped to the reset position, the latch of the circuit breaker is positioned in blocking relationship with respect to any possible movement of the cradle such that it is the latch which maintains the cradle in its latched or reset position against the bias of the now slightly extended main spring of the over-center mechanism.

This invention relates to circuit breakers and more particularly relates to the provision of mechanism within such circuit breakers whereby the circuit breaker will be automatically relatched to the circuit breaker open circuit or off position upon opening of the circuit breaker contacts in response to overload or fault currents.

Circuit breakers of the prior art generally are manually operable between three positions. Specifically, assuming the circuit breaker to be in the on position, that is, with the contacts closed and with the latching mechanism, to be hereinafter described, in its latched position, the occurrence of a prolonged overload or instantaneous fault current trips the latching mechanism whereby an overcenter spring operated mechanism snaps the circuit breaker movable contact to its open circuit position. The breaker is now in its tripped condition.

After the fault has been cleared and it is necessary to reestablish the circuit being protected, the following steps are normally required. First, the operating handle of the circuit breaker is moved from its stripped position (that is, the position the handle occupies with the circuit breaker contacts open and the latching mechanism tripped) to a reset position in which the latching mechanism is cocked for subsequent operation. In the reset position the movable contact of the circuit breaker remains open. Second, the operating handle is moved from the reset position back to the on position during which time the movable contact of the circuit breaker is snapped back into its closed circuit or on position.

In contradistinction thereto, the instant invention provides an automatic relatching system of simple construction whereby the circuit breaker will be automatically moved from its tripped to its reset and off position without the necessity of manually moving the operating handle between these positions. Thus, and in accordance with the instant invention, in response to' the occurrence of a fault, the circuit breaker will be tripped and sub-v Patented Dec. 10, 1968 ice sion spring which may be easily added to existing circuit breakers by relatively unskilled personnel.

As a particularly advantageous feature of the instant invention, and as will be discussed in greater detail, the instant invention is particularly applicable to certain types of circuit breakers whose particular over-center spring operated mechanisms advantageously necessitate a relatching spring of minimum spring force in order to accomplish the automatic relatching effected by the instant invention. Specifically, the circuit breakers in which the instant invention is partiularly applicable include overcenter spring operated mechanism, the main springs of which are only slightly extended when the latching mechanism is moved from its tripped to its reset position. Therefore, it will be apparent that the spring'force of the biasing means which accomplishes the automatic relatching feature of the instant invention need only be of a value suflicient to overcome the small spring force developed by the slightly extended main spring means as a result of the latching mechanism being moved from its tripped to its reset position.

Accordingly, it will be seen that it is an object of the instant invention to provide automatic relatching mechanism for circuit breakers whereby the circuit breaker will be automatically relatched to its open or reset position immediately subsequent to the tripping of such circuit breaker in response to the occurrence of fault conditions.

It is another object of the instant invention to provide such automatic relatching mechanism which is of simple construction and which may be assembled in existing circuit breakers with a minimum of effort and by relatively unskilled personnel.

It is another object of the instant invention to provide automatic relatching mechanism which is particularly applicable to circuit breakers including over-center spring operated mechanism the main springs of which are only slightly extended when the circuit breaker is moved between its tripped and reset positions whereby the spring of the automatic relatching mechanism need only have a spring force sufficient to overcome the small spring force developed by the slightly extended main spring means as a result of the latching mechanism being moved from its tripped to its reset position.

Other objects and a fuller understanding of the instant invention may be had by referring to the following specification and drawings, in which:

FIGURE 1 is a side view of a type of circuit breaker within which the instant invention is particularly applicable, with such circuit breaker being in the on position;

FIGURE 2 is a side view of the circuit breaker of FIGURE l, the mechanism of such circuit breaker momentarily occupying its tripped position;

FIGURE 3 is a side view of the circuit breaker of FIG- URES 1 and 2, but showing the circuit 'breaker operating mechanism occupying its reset and off. position;

FIGURE 3a is a detailed view of two of the parts shown in FIGURE 3 and illustrate-s the breaker being momentarily moved through its off position'in order to assure relatching;

FIGURE 4 is a side view of another type of circuit breaker within which the automatic relatching feature of the instant invention is particularly applica-ble, such circuit breaker ocoupying its on position;

FIGURE 5 is a side lview of the circuit breaker Ishown in FIGURE 4, but showing the internal mechanism of the circuit breaker momentarily occupying its tripped position; and

FIGURE 6 is a side view of the circuit breaker of FIG- URES 4 and 5, but showing the circuit breaker in its reset and off position.

Referring first to FIGURE l, there is shown a circuit breaker of a type with which the instant invention is preferably intended to cooperate. It should be noted that although only one circuit breaker 10 has been shown, and although the instant invention will be described with respect to onlyone such circuit breaker, such circuit breakers may be easily stacked in an assembly with their operating mechanisms appropriately connected to provide simultaneous protection for a plurality of circuits. Similarly, it is to be understood that the instant invention would be equally applicable to each circuit breaker of an arrangement comprising a plurality of circuit breakers 10.

Circuit breaker 10 comprises a base 18 of molded insulating material having an open side capped by a removable cover (not shown) which is also constructed of molded insulating material with the cover being Isecured to base 18 by rivets 21 which pass through circuit breaker 10. Stationary contact 22 is mounted to extension 23 of female stab type line terminal 24 which is disposed in a suitably shaped spaced recess. The lower end 25 of line terminal 24 is accessible through a suitable slot formed by the cooperation of the base 18 and the cover.

Cooperating with stationary contact 22 is movable contact 26 which is mounted to the lower end of movable contact arm 27 whose upper end abuts a suitable pivot forming formation of manual operating member 28. Parallel plate slotted arced extinguishing means 99 is operatively positioned to receive and extinguish electric current arcs drawn :between contacts 22, 26. Manual operating member 28 is pivoted about protrusions 29 thereof which is entered into suitable recesses of the base 18 and the cover (not shown).

Operating mechanism 30 for bringing about the engagement and disengagement of cooperating contacts 22, 26'comprises latchable cradle 31 which is pivoted at one end thereof at base protrusion 32. One end of cooperating spring 33 is tied to cradle 31 at a point intermediate the ends thereof while the other end of spring 33 is tied to contact arm 27. Operating spring 313 is tensioned, thereby urging contact arm 27 -upward into engagement with its pivot on manual operating member 28. The other end of cradle 31 comprises latch tip 34 which is engagcable by latch 3S secured to a thermal responsive control member 36 :by suitable fastening means.

Thermally responsive control member 36 comprises an elongated bimetallic element which is mounted near the upper end thereof to pivot pin 37. Magnet 38 is secured to control member 36 near the lower end thereof by suitable fastening means. Bifurcated member 39 is secured to control member 316 below magnet 38. Conducting braid 40a and 4Gb (40h not shown) extend from bifurcated member 39 to contact arm 27 and provide dual electrical paths between contact arm 27 and the bimetallic element 36.

Thermally responsive control member 36 is biased in a clockwise direction by pivot spring 40 which is disposed in a recess 40 of base 18 with one end of the spring 40 abutting wall 42 of recess `40 and the other end of spring 40 abutting the portion of thermally responsive control member 36 positioned above pivot 37.

When magnet 38 is energized sufliciently by current owing through thermally responsive control member 36, magnet 38 is attracted to armature 47 disposed in recesses provided in the base 1-8.

Flexible braid 57 electrically connects load terminal member 56 to thermally responsive control member 36. Terminal member 56 is entered into wire-connector 58 which is disposed within suitable recesses of base 18 and the matching cover.

Further details of the construction of the circuit breaker illustrated in FIGURES 1-3 may be had by referring to United States Patent 2,996,589, issued Aug. 15, 1961 to the assignee of the instant invention. Such patent is in` corporated herein by reference thereto.

Generally speaking, it may be seen that the current carrying path through circuit breaker 10, beginning at load side thereof, comprises terminal 56, braid 57 to the upper end of bimetallic thermally responsive control member 36, through control member 36 and bifurcated member 39, through the parallel paths formed by braids 40a, 4Gb, to contact arm 27 and through engaged cooperating contacts 26, 22 to line terminal 24.

In accordance with the instant invention an automatic relatching spring is secured at one end thereof to cradle 31 by suitable fastening means such as a hole 82 provided in cradle 31. The opposite end of spring 80 is similarly secured to a post 84 which is fixed on base 18. In the on position of FIGURE 1 (that is, with the contacts 22, 26 engaged), the spring `80 is relaxed. (Actually, the spring `80 may have a preloaded tension built in and therefore might not be completely relaxed.)

The operation of the instant invention as applicable within a circuit breaker such as the type described in the aforementioned United States Patent 2,996,589 and described herein will now be explained with reference to FIGURES 1, 2 and 3.

Assuming the breaker to occupy the on position shown in FIGURE 1, that is, with the contacts 22, 26 engaged and the cradle 31 maintained in its latched position by the interference of latch tip 34 and latch member 35, the occurrence of an overload in thermally responsive bimetallic control member 36, or the presence of a predetermined magnitude of fault current in magnet 38, will cause control member 36 to deflect or be rotated counterclockwise with respect to FIGURE 1 to free latch tip 34 from latch member 35. Cradle 31 under the biasing effect of main spring 33 now moves down to its releasing position during which time the spring 33 passes over-center whereby the the contact arm 27 will be snapped to its open circuit position and the circuit breaker will now go through its tripped position as shown in FIGURE 2. It will be appreciated that the main spring 33 in being moved from its position shown in FIGURE l to that shown in FIGURE 2, has expended virtually all its energy in opening the circuit breaker movable contact 26 and is now in its relaxed state. (The spring 33 may have a small preloaded tension built in and hence would not be completely relaxed.)

During the movement of cradle 31 from its position in FIGURE l to that in FIGURE 2, the biasing spring 80 has been extended from the position shown in FIGURE 1 to that shown in FIGURE 2. Consequently the spring force of biasing sp1-ing 80 pivots cradle 31 counter-clockwise about pivot point 32 to return the cradle 31 and latch tip 34 to its latched position wherein the latching member 35 obstructs the path of movement of the cradle (FIG- URE 3).

As indicated in FIGURE 3a, the latch tip 34 experiences a certain degree of over-travel to guarantee that the latching member 35 will be in its blocking position when the latch tip seats thereon.

As pointed out in the introductory remarks of this specication, the circuit breaker of the type illustrated in FIG- URES 1-3 is particularly advantageous for use with the instant invention. The reason for this will now be apparent. As most clearly seen in FIGURE 2, the latch tip 34 in travelling from its tripped position in FIGURE 2 to its latched position in FIGURE 3 under the influence of spring 80 moves a very small distance and hence the main spring 33 is only slightly extended during such movement. Stating it differently, it is noted that the arc of travel of the cradle is such that the distance between the spring holes in the cradle and contact arm is practically the same for both positions. Thus the maximum spring force of biasing spring 80 need only be a little greater than the spring force developed by main spring 33 in reaching this slightly extended position, thereby allowing the spring 80 to be relatively small and inexpensive.

During the movement of cradle 3.1 from its position in FIGURE 1 to FIGURE 2 and then `back to its latched position in FIGURE 3, the operating handle 28 has similarly moved from its position shown in FIGURE 1 through the position shown in FIGURE 2 to its position shown in FIGURE 3. Thus following the automatic relatching accomplished by the spring 80, the operating handle 28 assumes a position which indicates that the circuit breaker is in the open or off position, and is completely relatched for subsequent operation. To reclose the circuit, the operator merely moves the handle 28 from its position in FIGURE 2 back to the position shown in FIGURE 1 during which time the movable contact arm pivot is moved over-center to snap the contact arm into firm engagement with stationary contact 22.

Referring to FIGURES 4-6, there is shown a second type of circuit breaker within which the instant invention is primarily intended to cooperate. Although only one circuit breaker 100 is shown, it is to be understood that circuit breaker 100 is of the type which may be ganged to protect a multiphase circuit. The circuit breaker 100 is of the type shown in United States Patent 2,673,908, issued Mar. 30, 1954 in the name of J. C. Brumtield and assigned to the assignee of the instant invention. The overall description of such circuit breaker may be had by referring to such patent which is incorporated herein by reference thereto. For purposes of this invention it is suicient to note the overall circuit breaker and basic structure as follows.

The housing of circuit -breakers 100 is made of a plastic material, and is provided with appropriate openings 121 and 122 through which circuit breaker terminals 125 and 126, respectively, maybe brought out of the housing 120 to be engaged by the line terminal (not shown) of the line to be protected. Housing 120 consists of a base 120a and a cover 120b which completely encloses circuit breaker 100.

Circuit breaker terminal 125 extends through opening 121 into base .120a. Circuit breaker terminal 125 is shaped like an angle, one side of the angle being used to receive a line terminal (not shown) and the other side 131 is soldered or otherwise connected to a pigtail conductor 135.

Pigtail 135 is secured to the free end 137 of thermally responsive control member 138. Free end 137 is provided with a bolt 140and a nut 141. Extension 143 of bolt 140 serves a purpose hereinafter set forth.

Rivet 146 which serves to secure thermally responsive means 138 to angle 145 also serves to secure substantially rectangularly shaped magnet 150 to thermally responsive means 138.

The armature for magnet 150 is hook shaped and is loosely pivoted at its end 156 between the head of screw 147 and the head of rivet 146. The hook in armature 155 engages a hole 158 in one extension 160 of tripper bar 165.

When under fault current conditions, thermally responsive means 138 becomes operative, it will bend and will impart to extension 166 of tripper bar 165 an impact through extension 143 of screw 140.

If, on the other hand, magnet 150 becomes operative, it will pull toward itself armature 155 which being hooked to the extension 160 of tripper bar 165 will impart to tripper bar a rotation which, as shown, will be counterclockwise.

Pigtail 152 from fault current responsive means 138 and 150 is electrically connected in any suitable way to one end of movable contact arm 171. Movable contact arm 171 is pivoted at 172 to metallic frame or support 175. Contact arm 171 is provided at its other end with a substantially rectangular shaped contact 177.

Stationary contact .180 consists of a rectangular metallic member 181 having at the end near to contact arm 171 a Stationary contact pad 185. Stationary contact is also provided with a terminal extension 126, an integral part of the metallic member 181 which extends for a portion out of housing 120 to permit by means of screw means (not shown) a connection of a line terminal circuit breaker terminal 126.

Stationary contact 180 is also provided with an arc extinguishing chamber having a number of arc extinguishing plates 196, so that upon opening of the circuit breaker, the arc existing between contact 177 and contact pad 185 is extinguished before producing damage to the contacts 177 and 185.

`Contact arm 171 is provided near its center with a set of aligned openings which are engaged by a pin 201 (see FIGURE 4) carrying two metallic fingers 203 (see FIGURE 5) which comprises one portion of a circuit breaker toggle mechanism. The two linger members 203 which are secured to contact arm 171 by means of pin 201 are, therefore, rotatable with respect to contact arm 171 and an upward or downward motion of fingers 203 will be accompanied -by a rotation of contact arm 171 around its pivot 172.

The upper end of fingers 203 are provided with a pin 207 upon which one end of two linking members 210 are pivotally mounted. These two members 2110 comprise the other half of the aforementioned circuit breaker toggle mechanism.

One end of main spring 218 is secured to pin 207, while the other end of spring 218 secured to a T-shaped member 220 in its upper portion 222. T-shaped member 220 has two legs 225, one on each side of the toggle mechanism 203, 210. Legs 225 are provided with rivets 227 which engage U-shaped recesses, one on each side of frame 175.

T-shaped member 220 is provided at its upper portion 222 with extension 231. Upper portion 222 of T-shaped member 220 is slotted in its mid-portion and provided with raised portion 232 cut out from the upper portion of T-shaped member 220 which serves to engage a plastic operating handle 235 for manually opening and closing the circuit breaker as hereinafter described.

The upper end portion of linking members 210 are rotatably secured to an essentially V-shaped cradle 245 lby means of rivet 238. One leg 255 of cradle 245 is shaped as shown in FIGURES 4 and 6 to engage a latch 247. Latch 247 is provided with a slot 248 engaged by pin 250 around which latch 247 can rotate and can also have translational motion.

Latch 247 is provided with a pointed end latched under normal conditions by a latch surface 252 on tripper bar 165. The opposite leg of cradle 245 is pivotally mounted on frame 175 by pivot pin 260.

In accordance with the instant invention, spring 350 is secured at one end to end portion 255 of -cradle 245 while the opposite end of spring 350 is secured to the frame 175 by means such as post 352.

Referring to FIGURES 4-6, the operation of circuit breaker, shown therein, will now be described.

When the circuit breaker is in the open or off position but ready to be closed, or in other words not open because of fault current, latch surface 252 of tripper Vbar 165 engages the pointed end of latch 247 so that extension 255 of cradle 245 is in its latched position. Cradle 245 remains in the position of FIGURE 6 also when circuit breaker is manually closed by moving handle 235 from the position in FIGURE 6 to the position in FIG- URE 4.

When the handle 235 is moved from the position of FIGURE 6 to the position of FIGURE 4, it moves with it T-shaped member 220 which will rotate about pivot 227 and at an initial time will tension springs 218. When spring 218, now under tension, is moved through T-shaped member 220 over-center with respect to toggle 203, 210, a force is produced which urges members 210 and fingers 203 away from each other. When springs 218 go overcenter, they also bias T-shaped member 220 in a clockwise direction.

As toggle 203, 210 is being moved during the motion of T-shaped member 220 from left to right in FIGURE 6, fingers 203 push movable contact arm 171 and cause it to rotate about its pivot 172 into a high pressure engagement with stationary contact pad 185.

When it is desired to manually open the circuit breaker, handle 235 is moved from the position of FIGURE 4 to the position in FIGURE 6. After springs 218 have moved over-center through motion of T-shaped member 220, toggle 203, 210 will break and cause movable contact 271 to rotate about its pivot 72, thus opening the electrical circuit between contacts 177 and 185.

During both the opening and closing operations described above, cradle 245 does not move, but remains in its latched position because of the engagement of the latch tip of cradle 245 and the latch member 247.

Considering now the circuit breaker in its close'd position of FIGURE 4 and assuming that a fault current below a certain predetermined maximum value occurs, thermally responsive control means 138 will bend toward extension 166 of tripper bar 165 to cause tripper bar 165 to rotate counter-clockwise with respect to FIGURE 4. Counter-clockwise rotation of tripper bar 165 causes similar rotation of latching surface member 252, so as to allow latch member 247 to rotate counter-clockwise with respect to FIGURE 4. Cradle 245 is then set free to rotate in a clockwise direction with respect to FIGURE 5.

If the fault current had reached a predetermined magnitude, current flowing through magnet 150 would have drawn armature I155 and in so doing would have rotated tripper 165 to release cradle 245.

As cradle 245 rotates, it moves with it toggle 203, 210 and springs 218 so that springs 218 now break toggle 203, 210 and as previously described rotate contact arm 171 to its open circuit position. Also, and in an embodiment without relatching spring 350, because of the biasing action of springs 218, T-shaped member 220 and with it handle 235 will assume the position of FIG- URE 5.

It should be noted that the relatching spring 350 in FIGURE 4 is in a slightly extended preloaded tension condition, and that as the cradle 245 is freed in response to rotation of the latch member 247 caused by rotation of the tripper bar 165, the spring 350 is stretched as shown in FIGURE 5. Thus, when cradle 245 has reached its completely lreleased position, i.e., as shown in FIGURE 5, .and when spring 218 has been nearly exhausted, the biasing force of spring 350 automatically returns the cradle `245 to the position shown in FIGURE 6, wherein the cradle 2.45 is completely reset for subsequent operation. During the automatic resetting effected by biasing spring 350, contact arm 171 remains in its open circuit position, see FIGURES 5 and 6. As the biasing spring 350 is automatically returning the cradle to its latched position, handle 235, which is linked to cradle 245 through springs 218 and linking member 210 is automatically moved to the open or off position shown in FIGURE 6.

Thus, in order to re-establish the current path through the breaker, it is only necessary for the operator to move the circuit breaker handle from the position shown in FIGURE 6 to the position shown in FIGURE 4; thus, avoiding the step of manual reset which in the prior art would have required the operator to move the handle 235 from the position shown in FIGURE 5 to the position shown in FIGURE 6.

It is noted that the circuit breaker which has been described in FIGURES 4, 5 and 6 is particularly conducive to the addition of the automatic relatching spring of the instant invention. Specifically, when the circuit breaker latching mechanism has :achieved the position in FIGURE 5, with the springs 21'8 in their nearly relaxed state, it can be seen that the cradle 245 only has to be returned a short distance to be latched by latching member 247. (Compare the position of cradle 245 in FIGURES 5 and 6.) Thus, cradle 245 in moving from the position shown in FIGURE 5 to that in FIGURE 6, extends spring 218 by only a very slight amount. Therefore, the spring force of spring 350 need only be sufficient to overcome the spring force of spring 218 in this slightly extended position and may be relatively small.

Thus, there has been described a relatively simple and efiicient mechanism for automatically relatching a circuit breaker from its tripped to its open circuit or off position.

Although there has been described la preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited not by the specific disclosure herein, but only by the appending claims.

What is claimed is:

1. A circuit breaker comprising:

a casing;

an operating handle rotatably mounted on said casing for movement between a first and second position;

a stationary contact mounted on said casing;

a movable contact movable between a first position in which one end thereof is in engagement with said stationary contact and a second position in which said one end is out of engagement with said stationary contact;

over-center spring operated means connected between said movable contact and said operating handle for moving said movable contact between its first and second position in response to movement of said operating -handle between its first and second position, said over-center spring operated means including a cradle movable between a latched and releasing position, said cradle being normally biased toward its releasing position by main spring means of said over-center spring operator means, movement of said cradle between its latched and releasing position causing sai over-center spring operated means to move said movable contact from its first to its second position, said cradle beign pivotally monuted on said casing at one end thereof, the opposite end of said cradle terminating in a latch tip;

thermal responsive means pivotally mounted on said casing for movement between a first and second position in response to a predetermined current flow therethrough;

latch means, operable in response to movement of said thermal responsive means between its first and second position, between a rst position which obstructs the path of movement of said latch tip and thereby maintains said cradle in its latched position against the bias of said main spring means, :and a second position free of said latch tip such that said cradle may move to its releasing position to move said movable contact to its second position; and

bias means connected between said cradle and said casing for overcoming the bias of said main spring means to return said cradle to its latch position after it has moved to its releasing position; whereby said latch means will once again -maintain said cradle in its latched position against the bias of said main spring means.

2. The circuit breaker of claim 1, wherein said movable contact is pivotally secured at an opposite end thereof to said operating handle, and said main spring means is connected between said movable contact intermediate its ends thereof and said cradle, initial rotation of said operating handle between its second and first position with said cradle in its latched position causing said movable contact to be moved away from said cradle to elongate said main spring means, further rotation of said operating handle towards its first position causing said main spring means to pass a center position of maximum elongation corresponding to maximum spring force, after which said main spring means urges said movable contact into its first position, said main spring means remaining substantially extended when said movable contact is in its rst position;

movement of said latch means between its first and second position in response to movement of said thermal response means between its first land second position freeing said latch tip `whereby said cradle may move to its releasing position to move said main spring means back passed its center position and thereby move said movable contact to its second position, said main spring means being relaxed when said -cradle has completely reached its releasing position;

said bias means being extended upon movement of said cradle between its latched and releasing position, said bias means lreturning said cradle to its latched position after it has moved to its releasing position, movement of said cradle back to its latched position only slightly extending said main spring means whereby said bias means need only have a spring force when extended which is just greater than the spring force of said main spring means in its slightly extended position and whereby after said cradle is returned to its latched position by said bias means, said bias means is no longer required to hold said cradle in its latched position.

3. The circuit breaker of claim 2, and further including a. magnet secured to said thermal responsive means and movable therewith, an armature mounted to said casing, said latch means comprising a latch member secured to said thermal responsive means between said magnet Iand said thermal responsive means, said magnet and thermal responsive means being drawn towards said armature to move said latch member to its second position free of said latch tip so that said cradle may move to its releasing position in response to la predetermined fault current flowing through said magnet.

4. The circuit breaker of claim 1, wherein said mov- :able contact is pivotally mounted to a bracket which is secured to said casing, said over-center spring operated means includes a toggle mechanism comprising a finger member pi'votally mounted at one end thereof to said movable contact, and a linking `member pivotally mounted to the opposite end of said finger member at one end thereof :and pivotally mounted to said cradle at its opposite end thereof, said main spring means being secured to said operating handle at one end thereof and said finger member at said opposite end thereof;

initial rotation of said operating handle between its second and first position with said cnadle in its latched position causing said main spring means to be extended;

further rotation of said operating handle towards its first position causing said main spring means to pass a center position of maximum elongation corresponding to maximum spring force during which time said one end of said finger member and said opposite end of said linking member are urged away from each other to cause said movable contact to be moved to its first position, said main spring means remaining substantially extended when said movable contact is in its first position; movement of said latch means between its first and second position in response to movement of said thermal response means between its first and second position freeing said latch tip whereby said cnadle may move to its releasing position to move said main spring means back passed its center position and thereby urge said one end of said finger memberland said opposite end of said linking member toward each other to move said movable contact to its second position, said main spring means being completely relaxed when said cradle has completely lreached its releasing position; said bias means being extended upon movement of said cradle between its latched and releasing position, said bias means returning said cradle to its latched position after it has moved to its releasing position, movement of said cradle back to its latched position only slightly extending said m-ain spring means whereby said bias means need only have a spring force when extended which is just greater than the spring force of said main spring means in its slightly extended position, and whereby once said cradle is returned to its latched position, only said latch means maintains said cradle in said latched position against the bias of said main spring means. 5. The circuit breaker of claim 4, and further including -a magnet secured to said thermal responsive means, a trip lever rotatably mounted on said casing, :and an armature connected to said trip lever for rotation of said trip lever in response to movement of said armature towards said magnet caused by ia predetermined flow yof current through said magnet, said latch means comprising a latch member rotatably mounted on said casing, said latch member being maintained in its first position by la blocking latch surface of said trip lever, said latch member being free to assume its second position free of said latch tip of said cradle in response to rotation of said trip lever caused by movement of said armature towards said magnet.

References Cited UNITED STATES PATENTS 2,673,908 3/ 1954 Brumliel d. 3,081,386 3/1963 Koenig et al. 3,292,118 12/1966 Pastene.

BERNARD A. GILHEANY, Primary Examiner.

H. BROOME, Assistant Examiner.

U.S. Cl. X.R. 

